1. Field of the Invention
The present invention relates to an air conditioning system for a vehicle and, in particular, to a correction of a sun radiation sensor used in such an air conditioning system.
2. Description of Related Art
An independently controlled type of air conditioning system for a vehicle has been recently proposed, wherein different air conditioning zones in a cabin, such as a driver's zone and a passenger's zone, are subjected to independent control of an air conditioning requirement such as a discharged air temperature. Such an independent control of different zones in a vehicle is also required in the case of a so-called panel van type car. Namely, such a type of car has an increased cabin volume, so that independent air conditioning is frequently required in a front and rear zones of the cabin.
In such a independently controlled air condition system, in order to obtain precise air conditioning control in accordance with a air conditioning condition at a rear part of the cabin, the inventors of the present patent application have tested a sun radiation sensor which is arranged at the rear portion of the cabin for detecting a sun radiation amount introduced into the rear portion of the cabin. Furthermore, as a location for the sun radiation amount sensor suitable for the detection of the sun radiation onto a rear seat in the cabin, an inner wall of a rear hatch at an rear end of the cabin has been selected and a test has been done. According to the test, the inventors have found that the following problems occur. Namely, in the arrangement of the sun radiation sensor for detecting a sun radiation amount onto the rear seat of the cabin, a movement of the rear hatch, to open the latter, causes the rear seat sun radiation sensor to be moved together with the movement of the hatch. As a result, a difference is generated in a value of the incident angle of the sun radiation between the closed condition of the rear hatch and the opened condition of the rear hatch irrespective of a fact that the sun radiation amount is unchanged. Thus, a desirable detection of the sun radiation amount by the sun radiation sensor on the inner surface of the rear hatch is only possible at the closed condition of the rear hatch. When the rear hatch is moved to the open position, the detected value of the sun radiation amount by the sensor on the rear hatch is largely deviated from the sun radiation amount actually introduced onto the rear seat in the cabin. As a result, in a condition that the temperature of the cabin is controlled to a predetermined value with a small difference between the temperature inside the cabin and an outside air temperature, an opening of the rear hatch causes the sun radiation amount detected by the sun radiation sensor to be largely deviated from the actual value of the sun radiation amount, which prevents the air conditioning from being desirably controlled at the rear seat zone in the cabin.